The present invention relates to a focus control device, an endoscope system, a focus control method, and the like.
An endoscope system has been widely used that applies illumination light to tissue inside a body cavity, and allows the user to perform a diagnosis/procedure using image signals generated based on reflected light from the tissue. Since an endoscope optical system is normally designed to achieve deep focus with a deep depth of field, an image in which the object is in focus from the far point to the near point can be acquired during normal observation.
However, since the depth of field becomes shallow during zoom observation, the object may frequently become out of focus (defocused). In this case, since the user must perform a manual focus operation in order to observe the object using an in-focus endoscopic image, the burden imposed on the user increases.
An autofocus (AF) function may be introduced to solve the problem in which it is difficult to bring the object into focus during zoom observation. The user need not perform the manual focus operation as a result of introducing the AF function. For example, the endoscope system disclosed in JP-A-2002-258164 perform an AF operation during normal observation and zoom observation.
The AF operation (function) may be implemented using the optical system configuration illustrated in FIG. 19A or 19B. The configuration (single-lens drive configuration) illustrated in FIG. 19A is designed so that the in-focus object plane position is controlled by driving the zoom lens. Therefore, the magnification also changes when the in-focus object plane position is changed. The configuration (dual-lens drive configuration) illustrated in FIG. 19B is designed so that the zoom lens and the focus lens can be driven, and has an advantage in that the magnification and the in-focus object plane position can be controlled independently. However, the dual-lens drive configuration is complex as compared with the single-lens drive configuration. Therefore, it is difficult to implement the dual-lens drive configuration as compared with the single-lens drive configuration, and the diameter of the endoscope necessarily increases when the dual-lens drive configuration is incorporated in the endoscope.
Accordingly, it is desirable to employ the single-lens drive configuration illustrated in FIG. 19A for the endoscopic scope.